A Switch Mode Power Supply (SMPS) is a broad category of power supplies that are useful for applications requiring substantial amounts of power yet good regulation and control of the power delivered to the load. One such application includes plasma arc torches for welding and cutting of metallic workpieces. Switch mode power supplies are built around one or more switches or other switching elements.
Inductance based SMPS designs control the current flowing in an inductive element. The inductive element can take the form of an inductor, a transformer or both. The input control value of a switch is either ON or OFF. The ratio of the switch ON time to the sum of the ON time and OFF time is the duty cycle (D) of the switch.
A relationship can be developed between the duty cycle D and a regulated value, such as input or output voltage or current. This relationship is essentially linear over a finite range of operation. As long as the SMPS operates within the linear control range, classical control theory can be applied to the analysis and design of an inductance based, switch mode power supply.